The invention relates to teatcup liners for the milking of mammals, including cows, and more particularly to a teatcup liner maintaining desired mouthpiece chamber vacuum.
Milking systems withdraw milk from the milk secreting glands of mammals by applying negative pressure, i.e. vacuum, to the teat. A plurality of teatcups are provided, each having a liner around a respective teat, and defining a milk flow passage within the liner below the teat, and a pulsation chamber outside the liner between the liner and the teatcup. The milk flow passage within the liner supplies milk to a milking claw which also receives milk from the milk flow passages of other liners of other teatcups.
Simply supplying a constant vacuum to the teat is not desirable because it causes the tissue of the teat to become engorged with blood and lymph. When these fluids are confined to their normal spaces within the teat, the condition is described as congestion. When the fluids leave their normal spaces, it is described loosely as oedema. These conditions may result in pain or discomfort to the mammal being milked, and swelling of the tissue which may constrict the duct through which milk is being withdrawn, thereby slowing the flow of milk. The slowing of milk flow due to the effects of congestion may be accompanied by a reduced volume of milk available for removal because the discomfort may interfere with the milk ejection reflex by which the mammal presents her milk to the teat.
Various attempts have been made to ameliorate the undesirable effects of vacuum on the teat by carefully shaping the teatcup and liner to support the teat as well as possible, and by periodically relieving the vacuum to the teat. The liner periodically collapses around and below the teat, providing massage to the teat. The massage compresses the end of the teat, thereby acting as an "in-line pump" to move accumulated fluid from the tissues of the teat apex. The massaging action of the liner also provides stimulation to the teat whereby the milk ejection reflex is strengthened. In some cases, the milk ejection reflex may be elicited solely by the action of the pulsating liner. Various types of liners are known in the art, for example "A Comparison Of The Milking Characteristics Of Teat Cup Liners" I. McD. Gibb and G. A. Mein, The Australian Journal of Dairy Technology, December, 1976, pages 148-153, and U.S. Pat. Nos. 2,997,980, 3,096,740, 4,315,480, 4,324,201, 4,530,307, 4,745,881, 4,756,275 and 4,869,205. The milking cycle has an on portion and an off portion. Milk is withdrawn from the teat through the liner to the claw during the on portion. During the off portion, the closed liner stops milk flow from the teat.
A teatcup liner is provided by an elongated, flexible, generally tubular liner extending along a longitudinal axis. The liner has an upper section for mounting to a teat cup, a mouthpiece chamber including a shoulder below the upper section, and a barrel below the shoulder. The barrel may be of a smooth circular type, or may be fluted as in U.S. Pat. Nos. 4,530,307, 5,069,162. During peak milk flow, the smooth circular type liner typically has a mean mouthpiece chamber vacuum less than 10 kiloPascals, kPa, for a wide range of teat sizes, while the fluted type liner typically has a mean mouthpiece chamber vacuum in the range of about 20-30 kPa. The smooth circular type has a greater tendency to slip or fall off the teat. In "Design Of Milking Machines", O'Callaghan, Teagasc Dairy Production Research and Development Division, Moorepark, Fermoy, Co., Cork, Ireland, published at British Mastitis Conference 1993, it is indicated that high mouthpiece chamber vacuum levels, i.e. greater than 20 kPa, at the start of milking were associated with liners that gave good cluster stability, i.e. low slips. However, in "The Relationship Between Mouthpiece Vacuum, Teat Condition, and Udder Health", M. D. Rasmussen, National Mastitis Council Annual Meeting Proceedings, 1997, pp. 91-96, it is indicated that cows where high values of mouthpiece chamber vacuum were measured had poor udder health. In "Dynamic Testing During Milking, An Indicator of Teat Handling", M. D. Rasmussen et al., Danish Institute of Animal Science, Foulum, Denmark, published at Proc. Symp. Milk Synthesis, Secretion, And Removal In Ruminants, Univ. Beme, Switzerland, 1996, page 120, and National Mastitis Council Annual Meeting 1996, pages 170-171, it is indicated that teat diameter stayed the same after as before milking if the mouthpiece chamber vacuum was less than 20 kPa. The present inventor's conclusion from the various pieces of research is that a mean mouthpiece chamber vacuum greater than 20 kPa seems to be less comfortable to cows, results in more teat congestion and oedema, and has been linked to a higher rate of new mastitis infections. The goal of the present invention is to control the mouthpiece chamber vacuum within the range of 10-20 kPa, for a wide range of teat sizes and shapes, by changes in the teatcup liner geometry to produce a new liner with low slips and which milks cows gently and cleanly.
In U.S. Pat. No. 4,530,307, the flutes extend from just under the retaining ring at the upper section of the liner to the lower end of the barrel. In U.S. Pat. No. 5,069,162, the mouthpiece interior is fluted, and the mouthpiece exterior is smooth. In the present invention, it has been found that by eliminating the flutes on the interior surface of the wall of the mouthpiece chamber of the liner of the noted '162 patent, the mouthpiece chamber vacuum is maintained in the desired range of 10-20 kPa for a wide range of teat shapes and sizes. It is believed that this is caused by the smooth inside diameter at the shoulder of the mouthpiece chamber, instead of flutes, providing a more effective sealing of the teat against the inside of the liner, which in turn reduces the amount of vacuum applied to the teat in the region of the mouthpiece chamber. The mean observed value is in the range of 10-20 kPa, depending on teat size and length. The noted modification is accomplished by a rapid transition from the flutes in the barrel to a smooth inner diameter in the mouthpiece chamber at approximately the tangent point between the shoulder arc and the upper barrel.